Their findings coincided with an early-release report from the U.K. that showed women who took hormone replacement therapy (HRT) after menopause were 20 percent more likely to develop ovarian cancer or die from it than postmenopausal women who never took HRT.
The U.K. study, published online Wednesday by The Lancet, looked at the long-running Million Women Study and determined that 1,000 additional women died from ovarian cancer between 1991 and 2005 because they were using HRT, and that 1,300 extra cases of ovarian cancer were diagnosed in the same period.
For the U.S. study, experts suspect that HRT may have been fueling some breast cancers because that decline began soon after many women stopped using HRT.
"While there have been a number of theories put forward to explain the increase, it now looks like some of that increase is due to the use of HRT," Berry said. "When women stopped using HRT, it looked kind of like a market correction and the numbers went back down."
However, the WHI study, which included more than 16,000 postmenopausal women, was stopped early in May 2002 because HRT was increasing the risk of coronary disease, stroke and blood clots.
After the WHI trial was halted, many women stopped taking hormones. In fact, the use of HRT had dropped by 38 percent in the United States by the end of 2002. In 2001, 61 million prescriptions were written for hormone replacement therapy. In 2002, there were about 47 million prescriptions. By 2003, that number had fallen to 27 million, and by 2004 just 21 million, the study authors noted.
The rate of breast cancer started dropping soon after the WHI results in 2002, according to the new study.
Between 2001 -- the last full year of combination HRT use -- and 2004, rates of breast cancer in the United States dropped by 8.6 percent in postmenopausal women. The rates of estrogen receptor-positive breast cancer -- those cancers known to be fueled by the hormone estrogen -- dropped by 14.7 percent in women between the ages of 50 and 69. Yet, rates of estrogen receptor-negative cancers dropped only 1.7 percent in the same time period, which further suggests that stopping HRT played a role in the decline.
"HRT is probably not something that causes cancer; it probably just fuels existing cancers," explained Berry. "If you feed it, it grows, and if you stop feeding it, it stops growing."
Berry said the Emory researchers looked at other potential causes for the decline in breast cancer rates, including whether fewer women were getting screening mammograms to detect tumors. The researchers also checked for environmental factors and the use of breast cancer drugs such as tamoxifen and raloxifene. But none of these factors had changed significantly enough to cause such a drop in breast cancer rates, the study authors said.
The breast cancer rates leveled off by 2004, to rates not seen since 1987, the study authors said.
"Overall, this is very encouraging news," said Dr. Julia Smith, director of the New York University Cancer Institute Breast Cancer Screening and Prevention Program in New York City.
However, Smith said she'd like to know if this drop will affect survival rates in the future. "Have these cancers been eliminated, or are they just below our level of detection now, but will rise up again?" she asked.
Both Berry and Smith pointed out that if a woman is suffering through menopausal symptoms, such as hot flashes, short-term use of hormone replacement therapy is likely safe.
"You can give low-dose HRT for short periods of time for women who really have a quality-of-life issue," Smith said. She added that individual risk needs to be assessed on a case-by-case basis, but even some women at high risk of breast cancer may be able to use HRT for short-term relief.
"It doesn't make sense to do something in the name of prevention and protection -- (withholding HRT) -- that ends up hurting the person," Smith said.
Berry said: "If you're taking HRT for long-term health effects, it's not worth it. But, if you're taking HRT for menopausal symptoms and it works for you, it's probably a reasonable thing to continue. I'd stop it occasionally to see if the hot flashes are still there, but short-term use for a year or two probably won't affect your risk in the long run."
By Serena Gordon, HealthDay News, April 18, 2007